Hidden Alarm


  • 1

    Here are some of the materials you can use

    • 1 AA battery
    • AA battery holder (optional)
    • aluminum foil
    • 1 buzzer (preferably with wires attached) 
    • duct tape 
    • electrical wire (1–2 feet [30–70 cm]) (22-gauge works well)
    • paper
    • scissors
    • sheet of cardboard (non-corrugated, such as paperboard from cereal boxes)
    • wire strippers
  • 2

    Prepare ahead of time

    • Have paper and a pencil ready to write down ideas and sketches as you design.
    • Strip the plastic coating off the ends of your wire to expose the wire. This can be tricky, so you might want to have an adult help you with this step.
    • Think about alarms you have seen or have used. (Smoke alarm, snooze alarm, security alarm) How are they similar? (Buzzer, on-off switch)
  • 3

    Think about the challenge 

    • What is an alarm?
    • Why are many alarms hidden?
    • How does an alarm go on and off?
    • TIP: A circuit is a path that electricity can travel along. An alarm needs a circuit that can be opened and closed in order to work.
  • 4

    Think about and write down your ideas

    • Think of different places you might hide your alarm.
    • What size will your alarm need to be in order to fit in your hiding spot? 
    • How will you turn your alarm on and off? 
    • TIP: A switch starts and stops the flow of electricity. When the switch is closed, electricity flows to the buzzer and it buzzes and buzzes and buzzes. 
    • TIP: Inventors’ and engineers’ initial ideas rarely solve a problem. Instead, they try different ideas, learn from mistakes, and try again. The series of steps they use to arrive at a solution is called the design process.
  • 5

    Look at the materials

    • What materials do you need to make a closed circuit?
    • What materials can you use to make the alarm buzz?
    • How much wire do you need to hide your alarm?
    • How will you mount the parts of your hidden alarm?
    • TIP: An alarm needs a closed circuit in order to work. In a closed circuit, all the parts are connected and the electricity flows uninterrupted from the battery to the buzzer and back to the battery. In an open circuit, some parts are disconnected, and the gap prevents electricity from flowing.
  • 6

    Test the buzzer

    • Attach one end of the buzzer’s exposed wire to the battery.
    • Close the circuit by repeating on the opposite side of the battery.
    • TIP: Connect the buzzer, battery, and wires to make a closed circuit. The buzzer will buzz when you connect the pathway so the electricity can get from the battery to the buzzer. 
    • TIP: If the buzzer doesn’t work, check that the buzzer’s red wire is attached to the positive (+) side of the battery and the black wire to the negative (−) side. If not, reverse the wires and try again. 
  • 7

    Design and build the alarm 

    • Decide what materials you will use to make your alarm.
    • Think about what you need to build a circuit and mount it on.
    • Choose your materials and build the alarm.
    • TIP: Cardboard is stiff and can be used as a base. When folded, it can flex and act like a spring to open and close a circuit or to turn the alarm on and off.
    • TIP: A switch starts and stops the flow of electricity by closing and opening a gap in the circuit. 
    • TIP: Metal, such as the foil and wire, conducts, or transfers, electricity.
  • 8

    Build and test the switch

    • Decide how you will turn your buzzer on and off.
    • Build the switch.
    • Test the switch to be sure the buzzer works.
    • TIP: You can test an invention at different steps along the creation process. This way you can spot a problem when it happens instead of at the end of the process. 
  • 9

    Hide your alarm

    • Think of how you can surprise a friend with your hidden alarm.
    • Tape the alarm parts in your hiding spot. 
    • Add wire if you need length in order to hide your circuit.
    • TIP: If your alarm goes off before you finish hiding it, you may need to change the location where you place your alarm. And be sure to keep the circuit open until your friend closes the circuit by connecting the electrical pathway.  
  • 10

    Wait for the surprise

    • Make sure your alarm is in place.
    • Stand out of view and wait for the buzzer to go off.
    • TIP: If the buzzer doesn’t buzz, check for open connections that might cause a gap in the circuit. 
  • 11

    Did you know?

    • Smaller and Better
      Maybe the best things do come in small packages! Today, the average laptop computer weighs just 6 pounds (2.7 kg). (The very first computer, ENIAC, weighed 30 tons (30,000 km)—or as much as 10,000 laptops! And today’s laptops are even more powerful than ENIAC because the computer parts are much smaller and much faster. Just think, laptops and the alarm you made work in the same basic way—by switching circuits on and off.
  • 12

    Try this next!

    • Make it smaller and smaller. Redesign your alarm so that it’s even smaller than the one you made and can be hidden in a tighter spot.